KVM: PPC: Make PV mtmsr work with r30 and r31

So far we've been restricting ourselves to r0-r29 as registers an mtmsr
instruction could use. This was bad, as there are some code paths in
Linux actually using r30.

So let's instead handle all registers gracefully and get rid of that
stupid limitation

Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kernel/kvm_emul.S

@@ -135,7 +135,8 @@ kvm_emulate_mtmsr:
 
 	/* Find the changed bits between old and new MSR */
 kvm_emulate_mtmsr_reg1:
-	xor	r31, r0, r31
+	ori	r30, r0, 0
+	xor	r31, r30, r31
 
 	/* Check if we need to really do mtmsr */
 	LOAD_REG_IMMEDIATE(r30, MSR_CRITICAL_BITS)
@@ -156,14 +157,17 @@ kvm_emulate_mtmsr_orig_ins:
 
 maybe_stay_in_guest:
 
+	/* Get the target register in r30 */
+kvm_emulate_mtmsr_reg2:
+	ori	r30, r0, 0
+
 	/* Check if we have to fetch an interrupt */
 	lwz	r31, (KVM_MAGIC_PAGE + KVM_MAGIC_INT)(0)
 	cmpwi	r31, 0
 	beq+	no_mtmsr
 
 	/* Check if we may trigger an interrupt */
-kvm_emulate_mtmsr_reg2:
-	andi.	r31, r0, MSR_EE
+	andi.	r31, r30, MSR_EE
 	beq	no_mtmsr
 
 	b	do_mtmsr
@@ -171,8 +175,7 @@ kvm_emulate_mtmsr_reg2:
 no_mtmsr:
 
 	/* Put MSR into magic page because we don't call mtmsr */
-kvm_emulate_mtmsr_reg3:
-	STL64(r0, KVM_MAGIC_PAGE + KVM_MAGIC_MSR, 0)
+	STL64(r30, KVM_MAGIC_PAGE + KVM_MAGIC_MSR, 0)
 
 	SCRATCH_RESTORE
 
@@ -193,10 +196,6 @@ kvm_emulate_mtmsr_reg1_offs:
 kvm_emulate_mtmsr_reg2_offs:
 	.long (kvm_emulate_mtmsr_reg2 - kvm_emulate_mtmsr) / 4
 
-.global kvm_emulate_mtmsr_reg3_offs
-kvm_emulate_mtmsr_reg3_offs:
-	.long (kvm_emulate_mtmsr_reg3 - kvm_emulate_mtmsr) / 4
-
 .global kvm_emulate_mtmsr_orig_ins_offs
 kvm_emulate_mtmsr_orig_ins_offs:
 	.long (kvm_emulate_mtmsr_orig_ins - kvm_emulate_mtmsr) / 4